I am putting in a Crystal Pure SWG and was reading through the manual/install guide. I thought I had everything planned out but caught something on the second go around regarding the flow switch. First it requires 12 inches of straight length before it is in place with the cell itself counting as that if [placed inline right after. No big deal so I planned on putting it right after the cell. I caught a part in the guide that basically said if you have a spa with a spillover you should use option 2 or 3. Option 2 has the cell before the split valve and the flow switch on the pool return side past the valve. Option 3 has the cell and flow switch past the valve. It says the purpose is to prevent overchlorination when the spa is isolated. So my question is, is this really necessary for the short times that I have the spa isolated? I don't have an issue putting the flow switch after the valve but I will likely have to put in a new valve because everything is 1 1/2. I am going from 1 1/2 to 2 into the cell, and then going back down after the flow switch. To prevent going back and forth the only way is to replace the valve. The other challenge is where to put the flow switch if it does go past the valve. As seen in the picture below both pipes go down right after they split. I'd almost have to come off the valve, go horizontal for a foot before putting the switch in, and then tying back into the pipe a foot or two further down.
Another question I have is regarding a check-valve. Do I need to have one before the cell input? I'm sure it wouldn't hurt but I can't imagine anything could backflow from that into the heater that is before it.